AARS1-mediated lactylation reprograms macrophage lipid metabolism to restrict antitumor immunity.

BACKGROUND: Tumor-derived lactate has long been regarded as a metabolic waste product. However, accumulating evidence indicates that lactate also functions as a signaling molecule that actively remodels the tumor immune microenvironment. How lactate-driven post-translational modifications in immune cells contribute to immune evasion in hepatocellular carcinoma (HCC) remains incompletely understood. This study aimed to identify the immune cell population responsible for lactylation-driven immunosuppression in HCC and to elucidate the molecular mechanism by which lactylation rewires macrophage metabolism to impair CD8+ T cell-mediated antitumor immunity. METHODS: Selective in vivo immune cell depletion models were employed to define the key immune mediators of lactate-induced immunosuppression. Proteomic screening, site-directed mutagenesis, and lipidomic profiling were used to characterize lactylation targets and lipid metabolic alterations. Functional assays, including signaling pathway analyses, cytokine measurements, and tumor immune profiling, were performed in both in vitro systems and mouse HCC models. RESULTS: Macrophages were identified as the principal immune cell type mediating lactylation-dependent immunosuppression in HCC. Alanyl-tRNA synthetase 1 (AARS1) functioned as a non-canonical lactyltransferase, catalyzing lactylation of carnitine palmitoyltransferase 1A at lysine 675. This modification impaired long-chain fatty acid transport into mitochondria, leading to cytosolic accumulation of oleic acid (OA). OA directly disrupted cGAS binding to cytosolic DNA, thereby suppressing STING activation and type I interferon (IFN-I) production. Attenuated IFN-I signaling resulted in reduced major histocompatibility complex-I expression on tumor cells and impaired CD8+ T cell-mediated recognition and cytotoxicity. CONCLUSION: These findings uncover a lactate-lipid metabolism axis that links tumor-derived lactate to innate immune suppression in HCC. Targeting AARS1-mediated lactylation represents a potential therapeutic strategy to restore macrophage immunostimulatory function and enhance antitumor immunity.